The involutional phase (IDR) of proliferative diabetic retinopathy (PDR) is characterized by stable visual acuity and a marked decrease in the frequency of recurrent vitreous hemorrhages when compared to active PDR. Marked abnormalities of retinal function have been demonstrated, however, by color vision, visual field and electrophysiologic testing methods. Delayed implicit times observed in the electroretinogram (ERG) of all patients tested suggests that progressive loss of retinal functton will occur. Initial follow-up examinations have confirmed this hypothesis. The ERG b wave amplitude appears to be the most sensitive indicator of deterioration. Longitudinal studies are presently underway to determine the rate of deterioration of visual function in eyes with involutional diabetic retinopathy.